1. Field of the Invention
The present invention relates to an antenna device for use in a frequency band of a millimeter wave, also relates to a transmitting/receiving apparatus using the antenna device.
2. Description of the Related Art
There has been known an on-vehicle millimeter wave radar for use in a vehicle travelling on a road to measure a distance between this vehicle and another vehicle traveling ahead or behind, so as to measure a relative speed of this vehicle with respect to said another vehicle. Such millimeter wave radar, i.e., a transmitting/receiving apparatus consists of an integrally fabricated module including a millimeter wave oscillator, a circulator, a directional coupler, a mixer and an antenna device, with said transmitting/receiving apparatus being attached on the front or the rear portion of the vehicle.
The antenna device for use in the above millimeter wave radar consists of a primary radiator and a dielectric lens. A transmitting/receiving wave beam is formed by disposing the primary radiator in a focal point position of the dielectric lens.
However, the above conventional millimeter wave radar has at least the following problem which will be discussed in detail in the following. Namely, since the antenna device of the conventional millimeter wave radar has a fixed directivity, some predetermined detections and measurements will fail to be performed in a desired manner because of the restrictions of certain conditions. For instance, when a vehicle is running on a road having a plurality of traffic lanes, if the antenna device merely receives an electromagnetic wave reflected from another vehicle running ahead, it is still not possible to immediately determine whether or not the another vehicle is running along the same traffic lane on which this vehicle is running. Further, if a vehicle is running along a curved section or a waved section on a road, and if another vehicle running ahead of this vehicle along the same traffic lane is deviating from a detectable area, it is impossible to effect a desired detection.
Thus, in order to cope with the above problem, it is allowed to consider rotating an entire frame structure mounting the transmitting/receiving apparatus including the antenna device, so as to deflect the beam of an electromagnetic wave.
However, in use of such a rotatable structure, since an entire frame structure mounting the transmitting/receiving apparatus is required to be rotated, the apparatus as a whole will have to become large. Further, since movable parts of the apparatus have relatively large mass, it will be difficult to enable the beam of electromagnetic wave to scan at a high speed.